There continues to be a need for a continuous filter that, with little operator attention, will filter out particles as small as 0.45 microns. Most bacteria will be filtered out with a 0.45 micron pore size filter. The present invention covers use of a rotating, hollow, disc filter in which the disc may be covered with a membrane containing pores or openings of a controlled size that may be smaller than 0.3 microns.
We have considered the generalized patent issued to Breton, Ser. No. 3,997,447 which covers use of a rotating disc in a filter unit but differs in several unique aspects.
The present invention is intended to provide a unit that may be easily changed to cover many filtration needs. The objectives, then, of this invention include:
1. a filter that may with differing controlled pore-size plastic or sintered metal membrane covered rotating elements be used for such diverse purposes as filtering out bacteria, filtering oil out of water to extent of less than 0.1 ppm. oil remaining, filtering tails from beer manufacture to recover more of the desired product, filtering algae and fungi from water etc., etc.
2. a filter that will operate with very little back flushing and with very little, if any, manual cleaning for most operations
3. a low maintenance filter using well tested mechanical seals and corrosion resistant materials
4. a filter system with multiple filters and instrumentation to indicate leakage so that maintenance of one filter unit will reduce but not stop the flow to the system
5. a relatively low cost filter system.
To achieve these objectives the invention comprises hollow membrane covered discs mounted on a vertical hollow shaft in a cylindrical vessel; with means to rotate the shaft with discs installed and means to draw filtrate out of the center of the vertical hollow mounting shaft; and means to remove solids from the lower portion of the vessel and to draw lighter liquid fluids such as oil or lighter flocculent solids from the top of the vessel.
The hollow filter discs may be fabricated with the base of triangular shaped stiffener ribs welded to a central cylindrical hub containing vertical vent pipes and containing openings that will be adjacent to openings in a hollow rotatable mounting shaft when a plurality of discs are stacked vertically on the mounting shaft. One or more, usually four, vent pipes are formed in each hub. The ribs may be covered with a sintered metal layer or membrane which may have more or less controlled pore size of 2 to 50 microns or more. The sintered metal membrane on each side of the hollow disc being formed is also welded to the central cylindrical hub and the peripheral edges of the sintered metal membrane may be welded to each other or may be welded to an open metal "half pipe" or bead to form an expansion joint or may be clamped. Finally the sintered metal may be covered with a controlled porosity membrane that adheres to the sintered metal.
Note we have described one way of making the membrane covered disc. The disc may also be made by properly clamping the support metal and sintered metal membrane and controlled pore size plastic membranes together. The method of manufacture must be such as to have a disc that allows liquid to move into the center only thru the controlled pore-size sintered metal or plastic membrane, or thru both membranes and that maintains its structural integrity thru temperature change, rotation, and up to 150 p.s.i. pressure differential.
Feed liquid is introduced thru a feed manifold with a maximum of one feed line from the manifold between each adjacent pairs of discs. With the discs rotating the drag from each disc will cause the total mass of liquid to rotate so that as feed is jetted between plates, the heavier materials will be thrown outward by centrifugal force. The rotating disc is normally rotated at a speed to allow only a thin static layer at the surface of the disc The disc surface speed will be greatest at the periphery and least at the hub. The shaft size, disc size, rotational speed and viscosity of the liquid being filtered are all interrelated with the thickness of the static layer on each side of an operating disc. Some experimentation is necessary to optimize these variables for each feedstock.
Vent pipes thru the hub of each disc allow lighter oils to travel to the top of the vessel to be drawn off. With 10 psi pressure differential across a disc membrane with 0.5 micron pore size and 4" shaft with a 16" disc and 2000 rpm speed we have demonstrated filtration rates of 4 to 10 gallons per square foot of filter area per minute when filtering less than 2 ppm oil out of water.
Periodic cleaning of the filter discs may be accomplished using a centrufugal pump to pump filtrate back thru the hollow rotating shaft and thru the internal hollow disc upwards thru the membrane to dislodge any accumulation on the membrane. A draw off at the bottom of the unit may be valved back into the feed tank. The system may be simply automated to provide for cleaning when flow is restricted to a predetermined percentage of what is normal feed for a clean system or could be automated to backflush at set intervals in some visualized cases where filtration is quite difficult.